Method for making polymer solar cell

ABSTRACT

A method for making a polymer solar cell includes placing a carbon nanotube array into a polymer solution. The carbon nanotube array includes a plurality of carbon nanotubes. The polymer solution is cured to form a polymer layer. The polymer layer includes a first polymer surface and a second polymer surface opposite to the first polymer surface. Each of the plurality of carbon nanotubes includes a first carbon nanotube portion and a second carbon nanotube portion, the first carbon nanotube portion is embedded in the polymer layer, and the second carbon nanotube portion is exposed from the polymer layer. The second carbon nanotube portion is tilted on the first polymer surface to form a carbon nanotube layer. A cathode electrode is formed on a surface of the carbon nanotube layer away from the polymer layer. An anode electrode is formed on the second polymer surface.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is related to commonly-assigned applications entitled,“polymer solar cell”, concurrently filed on Oct. 10, 2018, withapplication Ser. No. 16/155,900; “METHOD FOR MAKING polymer solar cell”,concurrently filed on Oct. 10, 2018, with application Ser. No.16/155,894; “polymer solar cell”, concurrently filed on Oct. 10, 2018,with application Ser. No. 16/155,896; “polymer solar cell”, concurrentlyfiled on Oct. 10, 2018, with application Ser. No. 16/155,898; “METHODFOR MAKING polymer solar cell”, concurrently filed on Oct. 10, 2018,with application Ser. No. 16/155,899. Ser. No. 16/155,900 and Ser. No.16/155,894 share the same specification, Ser. No. 16/155,896 and Ser.No. 16/155,897 share the same specification, and Ser. No. 16/155,898 andSer. No. 16/155,899 share the same specification. Disclosures of theabove-identified applications are incorporated herein by reference.

FIELD

The present application relates to polymer solar cells and methods formaking the same.

BACKGROUND

The polymer solar cell has many advantages such as wide raw materialsand low cost, and has become one of the research hotspots in recentyears. When the light reaches the photoactive layer of the polymer solarcell, the photoactive layer absorbs photons of the light and generatesexcitons. The excitons diffuse and reach the interface between the donorand the acceptor to form electrons and holes. The electrons pass throughthe acceptor and reach the cathode electrode, and the holes pass throughthe donor and reach the anode electrode. Thus, a potential differencebetween the cathode electrode and the anode electrode is formed. The useof solar light is an important factor to affect the photoelectricconversion efficiency of the polymer solar cell. A common method is toincrease the solar light absorption rate by changing the material of thephotoactive layer.

Al-Haik et la. (US20070110977A1) discloses that a plurality of carbonnanotubes are dispersed in a polymer and then these carbon nanotubes areoriented using a magnetic field, to form a composite. The composite canbe acted as a photoactive material of the polymer solar cell. However,the carbon nanotubes are covered with the polymer, and the carbonnanotubes do not directly contact with the electrodes, thereby reducingthe electrical conductivity between the carbon nanotubes and theelectrodes.

Therefore, there is room for improvement in the art.

BRIEF DESCRIPTION OF THE DRAWINGS

Implementations of the present technology will now be described, by wayof example only, with reference to the attached figures, wherein:

FIG. 1 schematically shows a first embodiment of a polymer solar cell.

FIG. 2 schematically shows a first embodiment of one carbon nanotube ina polymer layer.

FIG. 3 is a process flow of a method for making the polymer solar cellof FIG. 1.

FIG. 4 is a process flow of the first embodiment of a method for placinga carbon nanotube array into a polymer solution.

FIG. 5 is a process flow of the first embodiment of another method forplacing the carbon nanotube array into the polymer solution.

FIG. 6 schematically shows the first embodiment of pressing the carbonnanotube array.

FIG. 7 schematically shows the first embodiment of rolling pressing thecarbon nanotube array.

FIG. 8 schematically shows the first embodiment of rolling pressing thecarbon nanotube array.

FIG. 9 is a process flow of another method for making the polymer solarcell of FIG. 1.

FIG. 10 schematically shows a second embodiment of a polymer solar cell.

FIG. 11 schematically shows a third embodiment of a polymer solar cell.

FIG. 12 schematically shows a fourth embodiment of a polymer solar cell.

DETAILED DESCRIPTION

It will be appreciated that for simplicity and clarity of illustration,where appropriate, reference numerals have been repeated among thedifferent figures to indicate corresponding or analogous elements. Inaddition, numerous specific details are set forth in order to provide athorough understanding of the embodiments described herein. However, itwill be understood by those of ordinary skill in the art that theembodiments described herein can be practiced without these specificdetails. In other instances, methods, procedures, and components havenot been described in detail so as not to obscure the related relevantfeature being described. The drawings are not necessarily to scale, andthe proportions of certain parts may be exaggerated to illustratedetails and features better. The description is not to be considered aslimiting the scope of the embodiments described herein.

Several definitions that apply throughout this disclosure will now bepresented.

The term “substantially” is defined to be essentially conforming to theparticular dimension, shape or other word that substantially modifies,such that the component need not be exact. For example, substantiallycylindrical means that the object resembles a cylinder, but can have oneor more deviations from a true cylinder. The term “comprising” means“including, but not necessarily limited to”; it specifically indicatesopen-ended inclusion or membership in a so-described combination, group,series and the like.

The disclosure is illustrated by way of example and not by way oflimitation in the figures of the accompanying drawings in which likereferences indicate similar elements. It should be noted that referencesto “an” or “one” embodiment in this disclosure are not necessarily tothe same embodiment, and such references mean at least one.

Depending on the embodiment, certain of the steps or blocks describedmay be removed, others may be added, and the sequence of steps or blocksmay be altered. It is also to be understood that the description and theclaims drawn to a method may include some reference numeral indicationreferring to certain blocks or steps. However, the reference numeralindication used is only for identification purposes and not interpretedas a suggestion as to an order for the steps.

FIG. 1 shows a polymer solar cell 100 of a first embodiment and thatincludes a support 10, an anode electrode 12, a photoactive layer 14,and a cathode electrode 18. The support 10, the anode electrode 12, thephotoactive layer 14, and the cathode electrode 18 are stacked on eachother in that order. The photoactive layer 14 includes a polymer layer142 and a plurality of carbon nanotubes 144 dispersed in the polymerlayer 142. A portion of each carbon nanotube 144 is exposed from thepolymer layer 142 and directly contacts the cathode electrode 18. In oneembodiment, the photoactive layer 14 consists of the polymer layer 142and the plurality of carbon nanotubes 144. Furthermore, the support 10can be omitted, because the photoactive layer 14 is a free-standingstructure.

The support 10 can be transparent or opaque. The material of the support10 can be glass, quartz, transparent plastic or resin. The material ofthe support 10 can also be silicon. The anode electrode 12 and thecathode electrode 18 can be a transparent conductive layer or a porousmesh structure, such as ITO (indium tin oxide) layer, FTO (F-doped tinoxide) layer, or the like. The anode electrode 12 and the cathodeelectrode 18 can be opaque, such as aluminum layer, silver layer, or thelike. When the cathode electrode 18 are transparent, the support 10 andthe anode electrode 12 can be transparent or opaque. When the cathodeelectrode 18 are opaque, the support 10 and the anode electrode 12 aretransparent. In one embodiment, light is irradiated to the photoactivelayer 14 through the support 10 and the anode electrode 12, the support10 is a glass plate, the material of the anode electrode 12 is ITO, andthe material of the cathode electrode 18 is aluminum.

The polymer layer 142 functions as an electron donor. The polymer layer142 has a first polymer surface 1422 and a second polymer surface 1424opposite to the first polymer surface 1422. The first polymer surface1422 is closed to the cathode electrode 18, and the second polymersurface 1424 directly contacts the anode electrode 12. The material ofthe polymer layer 142 can be polythiophene and its derivative,polyfluorene and its derivative, poly-phenylene vinylene and itsderivative, polypyrrole and its derivative, or any combination thereof.The polythiophene derivative can be poly(3-hexylthiophene) (P₃HT). Thepolyfluorene derivative can be poly(dioctylfluorene). The poly-phenylenevinylene derivative can bepoly[2-methoxy-5-(2-ethyl-hexyloxy)-1,4-phenylene vinylene]. In oneembodiment, the material of the polymer layer 142 is polythiophene.

The plurality of carbon nanotubes 144 functions as electron acceptors.FIG. 2 shows each carbon nanotube 144 consists of a first carbonnanotube portion 1446 and a second carbon nanotube portion 1448. Thefirst carbon nanotube portions 1446 of the plurality of carbon nanotubes144 are dispersed in the polymer layer 142, and substantially parallelto and spaced apart from each other. The lengths of the first carbonnanotube portions 1446 of the plurality of carbon nanotubes 144substantially extend along the same direction. The length direction ofthe first carbon nanotube portion 1446 is perpendicular to the firstpolymer surface 1422. The second carbon nanotube portions 1448 of theplurality of carbon nanotubes 144 are exposed from the polymer layer 142and directly contacts the cathode electrode 18. The second carbonnanotube portions 1448 are connected to each other to form a carbonnanotube layer 146. The carbon nanotube layer 146 is between the polymerlayer 142 and the cathode electrode 18. The carbon nanotube layer 146directly contacts the polymer layer 142 and the cathode electrode 18.

The carbon nanotube layer 146 is composed of a uniformly distributedplurality of second carbon nanotube portions 1448. The plurality ofsecond carbon nanotube portions 1448 are overlapped and connected toeach other by van der Waals force. An angle β is defined between theplurality of second carbon nanotube portions 1448 and the first polymersurface 1422, and 0°≤β≤60°. In one embodiment, 0°≤β≤15°. In oneembodiment, the plurality of second carbon nanotube portions 1448 lay onthe first polymer surface 1422, and the length directions of theplurality of second carbon nanotube portions 1448 are parallel to thefirst polymer surface 1422. The length directions of the plurality ofsecond carbon nanotube portions 1448 can be parallel to each other.Alternatively, the length directions of the plurality of second carbonnanotube portions 1448 are not be parallel to each other. That is, theplurality of second carbon nanotube portions 1448 can be orderly ordisorderly arranged. The term ‘disordered carbon nanotube’ refers to theplurality of second carbon nanotube portions 1448 are arranged alongmany different directions, and the aligning directions of the carbonnanotubes are random. The plurality of second carbon nanotube portions1448 arranged along each different direction can be almost the same(e.g. uniformly disordered). The plurality of second carbon nanotubeportions 1448 can be entangled with each other.

Each carbon nanotube 144 has a first end 1442 and a second end 1444opposite to the first end 1442. The first end 1442 can be locatedbetween and directly contact the first polymer surface 1422 and thecathode electrode 18. The second end 1444 is embedded in the polymerlayer 142, and does not directly contact with the anode electrode 12.The first carbon nanotube portions 1446 are embedded in the polymerlayer 142 and are not in contact with the anode electrode 12, such thatthe anode electrode 12 is electrically insulated from the carbonnanotubes 144. Thus, the electrons generated by exciton separation donot migrate from the carbon nanotubes 144 to the anode electrode 12. Allof the electrons generated by exciton separation can migrate from thecarbon nanotubes 144 to the cathode electrode 18.

The carbon nanotube layer 146 prevents the cathode electrode 18 fromdirectly contacting with the polymer layer 142. Thus, the holesgenerated by exciton separation do not migrate from the polymer layer142 to the cathode electrode 18. All of the holes can migrate from thepolymer layer 142 to the anode electrode 12. The carbon nanotubes 144can be single-walled, double-walled, multi-walled carbon nanotubes, ortheir combinations. The diameter of the single-walled carbon nanotubes144 are about 0.5 nanometers (nm) to about 50 nm. The diameter of thedouble-walled carbon nanotubes 144 are about 1.0 nm to about 50 nm. Thediameter of the multi-walled carbon nanotubes 144 are about 1.5 nm toabout 50 nm. The lengths of the carbon nanotubes 144 are substantiallyequal.

FIG. 3 shows the first embodiment of a method for making the polymersolar cell 100, and the method includes the following steps:

S11, placing the carbon nanotube array 20 into a polymer solution 22,wherein the carbon nanotube array 20 includes the plurality of carbonnanotubes 144 vertically located in the polymer solution 22, each carbonnanotube 144 has the first end 1442 and the second end 1444 opposite tothe first end 1442, the first end 1442 is exposed out of the polymersolution 22, and the second end 1444 is immersed in the polymer layer142;

S12, curing the polymer solution 22 to form the polymer layer 142,wherein the polymer layer 142 includes the first polymer surface 1422and the second polymer surface 1424 opposite to the first polymersurface 1422, and the plurality of carbon nanotubes 144 is verticallylocated in the polymer layer 142; each carbon nanotube 144 consists ofthe first carbon nanotube portion 1446 and the second carbon nanotubeportion 1448, the first carbon nanotube portion 1446 is embedded in thepolymer layer 142, the second carbon nanotube portion 1448 is exposedout of the polymer layer 142, and the length direction of the firstcarbon nanotube portion 1446 and the length direction of the secondcarbon nanotube portion 1448 are perpendicular to the first polymersurface 1422; and the first end 1442 is exposed out of the polymer layer142, and the second end 1444 is embedded in the polymer layer 142;

S13, tilting the second carbon nanotube portions 1448 that areoriginally perpendicular to the first polymer surface 1422, and makingthe second carbon nanotube portions 1448 and the first polymer surface1422 form the angle β (0°≤β≤60°), to form the carbon nanotube layer 146;

S14, forming the cathode electrode 18 on a surface of the carbonnanotube layer 146 away from the polymer layer 142;

S15, forming the anode electrode 12 on the support 10; and

S16, locating the second polymer surface 1424 on a surface of the anodeelectrode 12 away from the support 10.

In the step S11, the carbon nanotube array 20 has a first surface 202and a second surface 204 opposite to the first surface 202, and theplurality of carbon nanotubes 144 extend from the first surface 202 tothe second surface 204. The plurality of carbon nanotubes 144 aresubstantially parallel to and spaced apart from each other. The firstends 1442 of all of the carbon nanotubes 144 form the first surface 202,and the second ends 1444 of all of the carbon nanotubes 144 form thesecond surface 204. The length directions of the carbon nanotubes 144are substantially perpendicular to the first surface 202. In oneembodiment, the length directions of the carbon nanotubes 144 areperpendicular to the first surface 202, and the carbon nanotubes 144 areparallel to each other. The lengths of the carbon nanotubes 144 aregreater than or equal to 100 nanometers. In one embodiment, the lengthsof the carbon nanotubes 144 are several hundred micrometers to severalhundred millimeters. In one embodiment, the lengths of the carbonnanotubes 144 are greater than or equal to 100 micrometers and less thanor equal to 100 millimeters, such as 100 micrometers, 500 micrometers,1000 micrometers, or 5 millimeters.

The polymer solution 22 is formed by dispersing a polymer material in anorganic solvent. The organic solvent is not limited as long as thepolymer can be dissolved in the organic solvent. The method for placingthe carbon nanotube array 20 into the polymer solution 22 is notlimited. The present specification includes two methods, but is not solimited

FIG. 4 shows the first method for placing the carbon nanotube array 20into the polymer solution 22, and the method includes the followingsteps:

S111, growing the carbon nanotube array 20 on a growth substrate 30,wherein the first end 1442 of each carbon nanotube 144 directly contactsthe growth substrate 30, the second end 1444 of each carbon nanotube 144is away from the growth substrate 30;

S112, placing the polymer solution 22 in a container 28; and

S113, inverting the growth substrate 30 to make a portion of each carbonnanotube 144 immersed in the polymer solution 22, wherein the second end1444 is immersed in the polymer solution 22.

In the step S111, the method for making the carbon nanotube array 20includes the following steps: (a) providing a flat growth substrate 30,wherein the growth substrate 30 can be a P-type silicon wafer, an N-typesilicon wafer or a silicon wafer formed with an oxidized layer thereon;and in one embodiment, a 4-inch, P-type silicon wafer is used as thegrowth substrate 30; (b) forming a catalyst layer on the growthsubstrate 30, wherein the catalyst layer is made of a material selectedfrom the group consisting of iron (Fe), cobalt (Co), nickel (Ni), and analloy thereof; (c) annealing the growth substrate 30 with the catalystlayer in air at a temperature in a range from 700° C. to 900° C. forabout 30 minutes to about 90 minutes; (d) providing a carbon source gasat high temperature to a furnace for about 5 minutes to about 30 minutesto grow the carbon nanotube array 20 on the growth substrate 30.

In the step S113, the method for inverting the growth substrate 30 andpartially immersing the carbon nanotube array 20 into the polymersolution 22 is not limited. For example, the growth substrate 30 can befixed by a tool, such as tweezers, to invert the growth substrate 30.

It can be understood that, when the carbon nanotube array 20 is placedin the polymer solution 22 by the first method, it is necessary tofurther include a step of removing the growth substrate 30 before thestep S13. The method for removing the growth substrate 30 is notlimited, for example, the growth substrate 30 is peeled off using atool, such as a knife, or the growth substrate 30 is etched using alaser.

FIG. 5 shows the second method for placing the carbon nanotube array 20into the polymer solution 22, and the method includes the followingsteps:

S111′, growing the carbon nanotube array 20 on a growth substrate 30,wherein the first end 1442 of each carbon nanotube 144 directly contactsthe growth substrate 30, the second end 1444 of each carbon nanotube 144is away from the growth substrate 30;

S112′, removing the growth substrate 30;

S113′, placing the polymer solution 22 in the container 28; and

S114′, immersing a portion of each carbon nanotube 144 in the polymersolution 22.

In the step S112′, the carbon nanotube array 20 can be totally peeledoff from the growth substrate 30. In one embodiment, the carbon nanotubearray 20 is totally peeled off from the growth substrate 30 by a knifeor other similar tool along a direction parallel to the surface of thegrowth substrate 30. In the process of peeling off the carbon nanotubearray 20, adjacent two of the carbon nanotubes 144 join together by vander Waals attractive force, therefore the carbon nanotube array 20 isfree-standing structure. In one embodiment, two tweezers respectivelyclamp the two opposite sides of the carbon nanotube array 20.

The term “free-standing” includes, but not limited to, the carbonnanotube array 20 that does not have to be supported by a substrate. Forexample, a free-standing carbon nanotube array 20 can sustain itselfwhen it is hoisted by a portion thereof without any significant damageto its structural integrity. So, if the free-standing carbon nanotubearray 20 is placed between two separate substrates, a portion of thefree-standing carbon nanotube array 20, not in contact with the twosubstrates, would be suspended between the two substrates and yetmaintain structural integrity.

It can be understood that after curing the polymer solution 22 to formthe polymer layer 142 in the step S12 and before combining the polymerlayer 142 with the anode electrode 12 in the step S16, a step ofremoving the container 28 is needed. For example, the whole structure inthe container 28 is taken out of the container 28.

In the step S12, the method for curing the polymer solution 22 is notlimited, for example, polymer solution 22 is heated to form the polymerlayer 142.

In the step S13, the method for tilting the second carbon nanotubeportions 1448 is not limited. The present invention provides a methodfor tilting the second carbon nanotube portions 1448, but this methoddoes not limit the invention.

The method for tilting the second carbon nanotube portions 1448 includesthe following steps:

S131, providing a pressing device 40; and

S132, pressing the second carbon nanotube portions 1448 by the pressingdevice 40.

In the step S131, the pressing device 40 is a pressing head, and thesurface of the pressing head is smooth.

In the step S132, in the process of pressing the second carbon nanotubeportions 1448, the second carbon nanotube portions 1448 tilt such thatthe angle β (0°≤β≤60°) between the second carbon nanotube portions 1448and the first polymer surface 1422 is formed under the action ofpressure. The length directions of the second carbon nanotube portions1448 that originally perpendicular to the first polymer surface 1422 arechanged. In one embodiment, the second carbon nanotube portions 1448tilt to lay on the first polymer surface 1422 under the action ofpressure. The length directions of the second carbon nanotube portions1448 that originally perpendicular to the first polymer surface 1422 arechanged to be parallel to the first polymer surface 1422. When thesecond carbon nanotube portions 1448 tilt, the second carbon nanotubeportions 1448 are still joined to the first carbon nanotube portions1446, and the carbon nanotubes 144 are not broken by the pressure.

The length directions of the second carbon nanotube portions 1448 arecontrolled by the shape of the pressing head and the direction ofpressing. When the second carbon nanotube portions 1448 are pressed by aplanar pressing head along a direction perpendicular to the firstpolymer surface 1422, the second carbon nanotube portions 1448 randomlybent down and are entangled with each other to form a net-likestructure, as shown in FIG. 6. The net-like structure can be isotropic.When the second carbon nanotube portions 1448 are rolling pressed by aroller-shaped pressing head along a fixed direction, the second carbonnanotube portions 1448 tilt along the same direction, as shown in FIG.7. When the second carbon nanotube portions 1448 are rolling pressed bya roller-shaped pressing head along different directions, the secondcarbon nanotube portions 1448 tilt along different directions, as shownin FIG. 8. The carbon nanotube layer 146 has a certain thickness, andthe thickness of the carbon nanotube layer 146 can be controlled by theheights of the second carbon nanotube portion 1448 and the pressure.

In the step S14, the method for forming the cathode electrode 18 on thecarbon nanotube layer 146 is related to the distribution density of thesecond carbon nanotube portions 1448 in the carbon nanotube layer 146.When the distribution density of the second carbon nanotube portions1448 in the carbon nanotube layer 146 is large, such that there is nothrough hole that can penetrate entire carbon nanotube layer 146, thecathode electrode 18 can formed on the surface of the carbon nanotubelayer 146 away from the polymer layer 142 by sputtering, coating, vapordeposition, spraying, or the like. The cathode electrode 18 does notdirectly contact with the polymer layer 142, because there is no thethough hole in the carbon nanotube layer 146 and the material of thecathode electrode 18 does not pass through the carbon nanotube layer 146to directly contact with the polymer layer 142. When the distributiondensity of the second carbon nanotube portions 1448 in the carbonnanotube layer 146 is small, such that a gap is formed between twoadjacent second carbon nanotube portions 1448, a previously preparedcathode electrode 18, such as a metal film, is placed on the surface ofthe carbon nanotube layer 146 away from the polymer layer 142.

Under the same pressure, the distribution density of the second carbonnanotube portions 1448 in the carbon nanotube layer 146 is related tothe distribution density of the carbon nanotubes 144 in the carbonnanotube array 20. The distribution density of the carbon nanotubes 144in the carbon nanotube array 20 is larger, and the distribution densityof the second carbon nanotube portions 1448 in the carbon nanotube layer146 is larger. The distribution density of the carbon nanotubes 144 inthe carbon nanotube array 20 is smaller, and the distribution density ofthe second carbon nanotube portions 1448 in the carbon nanotube layer146 is smaller.

In the step S15, the method for forming the anode electrode 12 on thesupport 10 is not limited, such as sputtering, coating, vapordeposition, mask etching, spraying, or inkjet printing.

In the step S16, the method for locating the second polymer surface 1424on the surface of the anode electrode 12 away from the support 10 is notlimited. For example, the second polymer surface 1424 of the polymerlayer 142 is adhered to the anode electrode 12 by conductive adhesive.Alternatively, the product prepared in the step S14 and the productprepared in the step S15 can be combined to form an integrativestructure by hot pressing or cold pressing.

In one embodiment, the hot pressing is used. The product prepared in thestep S14 is stacked with the product prepared in the step S15 to form astacked structure. The stacked structure is placed in a hot pressingdevice including a metal roll and a heating element. The metal roll isheated by the heating element, and the heating temperature can softenthe anode electrode 12 and the polymer layer 142. And then the heatedmetal roll presses the stacked structure such that a pressure is appliedon the stacked structure. During pressing the stacked structure by theheated metal roll, the anode electrode 12 and the polymer layer 142 canbe softened and the air in the micropores of the stacked structure canbe expelled. Thus, the anode electrode 12 and the polymer layer 142 canbe closely pressed together. A rolling speed of the metal roll can be ina range from about 1 millimeter per minute to about 10 meters perminute. The pressure applied by the metal roll can be in a range fromabout 5 Pa to about 100 Pa. It can be understood that the temperature ofthe metal roll should be low enough so that the anode electrode 12,polymer layer 142, and other functional layers do not melt.

It can be understood that the anode electrode 12 can also be directlyformed on the second polymer surface 1424 of the polymer layer 142 bysputtering, coating, evaporation, or the like. And then the support 10is located on the anode electrode 12 away from the polymer layer 142.Furthermore, the anode electrode 12 is directly formed on the secondpolymer surface 1424 being free-standing structure, thus the support 10that plays a supporting role can be omitted, and the step of disposingthe support 10 can also be omitted.

It can be understood that the cathode electrode 18 is formed on thesurface of the carbon nanotube layer 146 away from the polymer layer 142to form a composite structure. Then, the support 10, the anode electrode12, and the composite structure are sequentially stacked together. Theanode electrode 12 is located between the support 10 and the secondpolymer surface 1424 of the polymer layer 142.

When any one of the anode electrode 12 and the cathode electrode 18 is ametal film, the metal film can reflect light that reaches the metal filminto the photoactive layer 14, improving the utilization of light. Thus,the metal film plays an electric conducting and reflecting light role.

FIG. 9 shows the first embodiment of another method for making thepolymer solar cell 100, and the method includes the following steps:

S11′, placing the support 10 in a container 28, wherein the anodeelectrode 12 is formed on a surface of the support 10 away from thecontainer 28;

S12′, placing the polymer solution 22 in the container 28, wherein inone embodiment, the polymer solution 22 is located on a surface of theanode electrode 12 away from the support 10;

S13′, locating the carbon nanotube array 20 in the polymer solution 22,wherein the carbon nanotube array 20 includes the plurality of carbonnanotubes 144, each of the plurality of carbon nanotube 144 has thefirst end 1442 and the second end 1444 opposite to the first end 1442,the first end 1442 is exposed out of the polymer solution 22, and thesecond end 1444 is immersed in the polymer layer 142;

S14′, curing the polymer solution 22 to form the polymer layer 142,wherein the polymer layer 142 includes the first polymer surface 1422and the second polymer surface 1424 opposite to the first polymersurface 1422, and the plurality of carbon nanotubes 144 is verticallylocated in the polymer layer; each carbon nanotube 144 consists of thefirst carbon nanotube portion 1446 and the second carbon nanotubeportion 1448, the first carbon nanotube portion 1446 is embedded in thepolymer layer 142, the second carbon nanotube portion 1448 is exposedout of the polymer layer 142, and the length direction of the firstcarbon nanotube portion 1446 and the length direction of the secondcarbon nanotube portion 1448 are perpendicular to the first polymersurface 1422; and the first end 1442 is exposed out of the polymer layer142, and the second end 1444 is embedded in the polymer layer 142;

S15′, tilting the second carbon nanotube portions 1448 that areoriginally perpendicular to the first polymer surface 1422, and makingthe second carbon nanotube portions 1448 and the first polymer surface1422 form the angle β (0°≤β≤60°), to form the carbon nanotube layer 146;and

S16′, forming the cathode electrode 18 on a surface of the carbonnanotube layer 146 away from the polymer layer 142.

The method as shown in FIG. 9 is similar to the method as shown in FIG.3 above except that the support 10 and the anode electrode 12 arelocated in the container 28, and then the polymer solution 22 is pouredinto the container 28; and finally the carbon nanotube array 20 and thecathode electrode 18 are formed in that order.

In the step S12′, the polymer solution 22 may flow between the support10 and the sidewall of the container 28, and between the anode electrode12 and the sidewall of the container 28 along the sidewall of thecontainer 28. After curing the polymer solution 22, the polymer layer142 can be also present between the support 10 and the sidewall of thecontainer 28, and between the anode electrode 12 and the sidewall of thecontainer 28. After removing the container 28, the polymer layer 142 ison the opposite sides of the support 10 and the anode electrode 12,thereby increasing the bonding force between the support 10, the anodeelectrode 12, and the polymer layer 142. Alternatively, the polymerlayer 142 on the opposite sides of the support 10 and the anodeelectrode 12 can be removed by etching.

The support 10 in the step S11′ can be omitted, and the anode electrode12 is directly formed at the bottom of the container 28. The container28 can be removed after forming the cathode electrode 18.

FIG. 10 shows a polymer solar cell 200 of a second embodiment. Thepolymer solar cell 200 of the second embodiment is similar to thepolymer solar cell 100 of the first embodiment above except that thepolymer solar cell 200 further includes a reflective layer 24 located onthe surface of the cathode electrode 18 away from the carbon nanotubelayer 146. In the second embodiment, the support 10 is transparent, andthe surface of the support 10 away from the anode electrode 12 is theincident surface of light. When the cathode electrode 18 is transparentand the surface of the cathode electrode 18 away from the carbonnanotube layer 146 is the incident surface of light, the reflectivelayer 24 is located on the surface of the support 10 away from the anodeelectrode 12.

The function of the reflective layer 24 is: when light reaches thephotoactive layer 14 from the transparent support 10, part of the lightthat reaches the cathode electrode 18 can be reflected back into thephotoactive layer 14 from the cathode electrode 18 by the reflectivelayer 24 located on the surface of the cathode electrode 18 away fromthe carbon nanotube layer 146. Thus, the utilization of light isimproved. When light reaches the photoactive layer 14 from the cathodeelectrode 18, part of the light that reaches the support 10 can bereflected back into the photoactive layer 14 from the support 10 by thereflective layer 24 located on the surface of the support 10 away fromthe anode electrode 12. Thus, the utilization of light is improved. Thematerial of the photoactive layer 14 has a high reflectivity, and thematerial can be, but is not limited to, a metal or metal alloy. Themetal can be gold, silver, aluminum, or calcium. The metal alloy can bean alloy of calcium and aluminum, an alloy of magnesium and silver, orthe like.

In the second embodiment, the method for making the polymer solar cell200 is provided. The method for making the polymer solar cell 200 in thesecond embodiment is similar to the method for making the polymer solarcell 100 in the first embodiment above except that the method for makingthe polymer solar cell 200 further includes a step of forming thereflective layer 24. When the support 10 is transparent, the reflectivelayer 24 is formed on the surface of the cathode electrode 18 away fromthe carbon nanotube layer 146 by sputtering, coating, vapor deposition,or the like. When the cathode electrode 18 is transparent, thereflective layer 24 is formed on the surface of the support 10 away fromthe anode electrode 12 by sputtering, coating, vapor deposition, or thelike.

FIG. 11 shows a polymer solar cell 300 of a third embodiment. Thepolymer solar cell 300 of the third embodiment is similar to the polymersolar cell 100 of the first embodiment above except that the polymersolar cell 300 further includes an exciton blocking layer 26. Theexciton blocking layer 26 can be located between the photoactive layer14 and the anode electrode 12. The exciton blocking layer 26 can also belocated between the carbon nanotube layer 146 and the cathode electrode18.

The function of the exciton blocking layer 26 is: light reaches thephotoactive layer 14 to form excitons, and the exciton blocking layer 26prevents the excitons from diffusing toward the cathode electrode 18 orthe anode electrode 12, thereby making all excitons reach the interfacebetween the donor and the acceptor. Thus, the utilization ratio of theexcitons is improved, and accordingly the efficiency of photoelectricconversion of the polymer solar cell 300 is also improved. The materialof the exciton blocking layer 26 is organic material, such asZn₄O(AID)₆, BAlQ₃, BCP, Bphen, Alq₃, TAZ, or TPBI.

In the third embodiment, the method for making the polymer solar cell300 is provided. The method for making the polymer solar cell 300 in thethird embodiment is similar to the method for making the polymer solarcell 100 in the first embodiment above except that the method for makingthe polymer solar cell 300 further includes a step of forming theexciton blocking layer 26. After the step S13 and before the step S14,the exciton blocking layer 26 is formed on the carbon nanotube layer 146away from the polymer layer 142 by sputtering, coating, vapordeposition, or the like. Alternatively, before combining the secondpolymer surface 1424 with the surface of the anode electrode 12 awayfrom the support 10, the exciton blocking layer 26 is formed on thesecond polymer surface 1424 by sputtering, coating, vapor deposition, orthe like.

FIG. 12 shows a polymer solar cell 400 of a fourth embodiment. Thepolymer solar cell 400 of the fourth embodiment is similar to thepolymer solar cell 100 of the first embodiment above except that thearrangement of the carbon nanotubes 144. In the polymer solar cell 100of the first embodiment, the length directions of the first carbonnanotube portions 1446 are substantially perpendicular to the firstpolymer surface 1422 of the polymer layer 142. In the polymer solar cell400 of the fourth embodiment, the length directions of the first carbonnanotube portions 1446 and the first polymer surface 1422 form an anglethat is greater than 0 degrees and less than 90 degrees. In oneembodiment, the angle is greater than 30 degrees and less than 60degrees. In one embodiment, the angle is greater than 0 degrees and lessthan 15 degrees. The advantage of the polymer solar cell 400 is: thefirst carbon nanotube portions 1446 are tilted in the polymer layer 142,thus the surface of the carbon nanotubes 144 (acceptor) in contact withthe polymer layer 142 (donor) is increased. It is beneficial forseparating more excitons to form electrons and holes. Thus, thephotoelectric conversion efficiency of the polymer solar cell 400 isimproved.

In the fourth embodiment, the method for making the polymer solar cell400 is provided. The method for making the polymer solar cell 400 in thefourth embodiment is similar to the method for making the polymer solarcell 100 in the first embodiment above except that the method for makingthe polymer solar cell 400 further includes a step of pressing thecarbon nanotube array 20 before curing the polymer solution 22 orplacing the carbon nanotube array 20 in the polymer solution 22. Thecarbon nanotube array 20 can be pressed by a pressing device 40, suchthat the carbon nanotubes 144 tilt. The degree of inclination of thecarbon nanotubes 144 can be controlled by controlling the pressure, suchthat the angle of grater than 0 degrees and less than 90 degrees isformed between the first polymer surface 1422 and the first carbonnanotube portions 1446.

The polymer solar cells 100 to 400 have the following advantages: 1) thesecond carbon nanotube portions 1448 are exposed from the polymer layer142 and directly contact the cathode electrode 18, improving theelectrical conductivity between the carbon nanotubes 144 and the cathodeelectrode 18; 2) the carbon nanotubes 144 of the carbon nanotube array20 are aligned themselves, and it is no longer necessary to orient thecarbon nanotubes 144 by external force, such as a magnetic field.

The embodiments shown and described above are only examples. Even thoughnumerous characteristics and advantages of the present technology havebeen set forth in the foregoing description, together with details ofthe structure and function of the present disclosure, the disclosure isillustrative only, and changes may be made in the detail, including inmatters of shape, size and arrangement of the parts within theprinciples of the present disclosure up to, and including, the fullextent established by the broad general meaning of the terms used in theclaims.

Additionally, it is also to be understood that the above description andthe claims drawn to a method may comprise some indication in referenceto certain steps. However, the indication used is only to be viewed foridentification purposes and not as a suggestion as to an order for thesteps.

What is claimed is:
 1. A method for making a polymer solar cell,comprising: placing a carbon nanotube array into a polymer solution,wherein the carbon nanotube array comprises a plurality of carbonnanotubes, a portion of each of the plurality of carbon nanotubes isimmersed in the polymer solution; curing the polymer solution to form apolymer layer, wherein the polymer layer comprises a first polymersurface and a second polymer surface opposite to the first polymersurface, each of the plurality of carbon nanotubes comprises a firstcarbon nanotube portion and a second carbon nanotube portion, the firstcarbon nanotube portion is embedded in the polymer layer, and the secondcarbon nanotube portion is exposed from the polymer layer; tilting thesecond carbon nanotube portion on the first polymer surface to form acarbon nanotube layer; forming a cathode electrode on a surface of thecarbon nanotube layer away from the polymer layer; and forming an anodeelectrode on the second polymer surface.
 2. The method of claim 1,wherein placing the carbon nanotube array into the polymer solution isperformed by vertically immersing the plurality of carbon nanotubes inthe polymer solution.
 3. The method of claim 2, wherein lengthdirections of the plurality of carbon nanotubes is substantiallyperpendicular to the first polymer surface when the plurality of carbonnanotubes are vertically immersed in the polymer solution.
 4. The methodof claim 1, wherein after curing the polymer solution and before tiltingthe second carbon nanotube portion, the length directions of the firstcarbon nanotube portion and the second carbon nanotube portion aresubstantially perpendicular to the first polymer surface.
 5. The methodof claim 1, wherein after tilting the second carbon nanotube portion,the length direction of the second carbon nanotube portion is changedfrom substantially perpendicular to the first polymer surface toparallel to the first polymer surface.
 6. The method of claim 1, whereinafter tilting the second carbon nanotube portion, an angle β is formedbetween the second carbon nanotube portion and the first polymersurface, and 0°≤β≤60°.
 7. The method of claim 1, wherein tilting thesecond carbon nanotube portion comprises pressing the second carbonnanotube portion by a planar pressing head along a directionperpendicular to the first polymer surface.
 8. The method of claim 7,wherein after tilting the second carbon nanotube portion, a plurality ofsecond carbon nanotube portions are entangled with each other to form anet-like structure.
 9. The method of claim 1, wherein tilting the secondcarbon nanotube portion comprises roll pressing the second carbonnanotube portion using a roller-shaped pressing head along a direction.10. The method of claim 9, wherein after tilting the second carbonnanotube portion, length directions of a plurality of second carbonnanotube portions extend along the same direction.
 11. The method ofclaim 1, wherein tilting the second carbon nanotube portion comprisesroll pressing the second carbon nanotube portion using a roller-shapedpressing head along different directions.
 12. The method of claim 11,wherein after tilting the second carbon nanotube portion, lengthdirections of a plurality of second carbon nanotube portions extendalong different directions.
 13. The method of claim 1, furthercomprising pressing the carbon nanotube array before placing the carbonnanotube array in the polymer solution, to tilt the plurality of carbonnanotubes.
 14. The method of claim 13, wherein an angle greater than 0degrees and less than 90 degrees is formed between the first polymersurface and the plurality of the carbon nanotubes.
 15. A method formaking a polymer solar cell, comprising: placing an anode electrode in acontainer; placing a polymer solution in the container, wherein thepolymer solution is located on the anode electrode; placing a carbonnanotube array into the polymer solution, wherein the carbon nanotubearray comprises a plurality of carbon nanotubes, a portion of each ofthe plurality of carbon nanotubes is immersed in the polymer solution;curing the polymer solution to form a polymer layer, wherein the polymerlayer comprises a first polymer surface and a second polymer surfaceopposite to the first polymer surface, each of the plurality of carbonnanotubes comprises a first carbon nanotube portion and a second carbonnanotube portion, the first carbon nanotube portion is embedded in thepolymer layer, and the second carbon nanotube portion is exposed fromthe polymer layer; tilting the second carbon nanotube portion on thefirst polymer surface to form a carbon nanotube layer; and forming acathode electrode on a surface of the carbon nanotube layer away fromthe polymer layer.
 16. The method of claim 15, wherein tilting thesecond carbon nanotube portion comprises pressing the second carbonnanotube portion by a planar pressing head along a directionperpendicular to the first polymer surface.
 17. The method of claim 15,wherein tilting the second carbon nanotube portion comprises rollpressing the second carbon nanotube portion using a roller-shapedpressing head along a direction.
 18. The method of claim 15, whereintilting the second carbon nanotube portion comprises roll pressing thesecond carbon nanotube portion using a roller-shaped pressing head alongdifferent directions.
 19. The method of claim 15, wherein after tiltingthe second carbon nanotube portion, the length direction of the secondcarbon nanotube portion is changed from substantially perpendicular tothe first polymer surface to parallel to the first polymer surface. 20.The method of claim 15, wherein after tilting the second carbon nanotubeportion, an angle β is formed between the second carbon nanotube portionand the first polymer surface, and 0°≤β≤60°.